Dehydration is a state defined by tilting of the normal balance of water and/or electrolytes and salts towards depletion. Water in the body is found in complex with salts and ions. It is distributed in spaces around the cells; the extracellular compartment, and the fluid content within cells is termed as intracellular. The movement of water molecules through the cellular membranes also attracts ions and electrolytes with it. Sodium is the primary ion in the extracellular fluid while calcium is its corresponding anion. Potassium plays role in the intracellular compartment of water. 
The body can have depleted stores of water and ions; when the intake of water is not adequate to meet the body’s demands, or if there has been an excessive abnormal loss of water that cannot be compensated by mere intake of water. Normally, the human body can lose 1.5 liters per day of water and its associated salts and ions in the urine via the urinary tract. Water is also lost in feces via the gastrointestinal tract, and as sweating through the skin. The imperceptible evaporation of water from the skin and lungs comes under the heading of insensible water loss, which amounts to 0.9 liters per day. If this loss is not compensated by adequate intake of water, dehydration results. A person may lose about 50ml/kg of body fluids to more than 100ml/kg which presents as mild, moderate or severe dehydration.